The atomization of liquid injected under pressure through an orifice is a process frequently found in many industrial processes, such as painting, and fuel injection. A simple system producing a good dispersion, and maintaining a clog-free operation, is being sought in these fields. In order to reduce particular emissions from diesel engines, it is convenient to improve the dispersion of the fuel injected near the end of the compression stroke. Current injection processes attempt to achieve this by multiplying the number of spray plumes produced within the combustion chamber (multiorifice injectors), by imparting a vigorous swirling motion to the air contained in the cylinder, or by injecting the fuel against a highly heated wall, where it quickly vaporized (indirect injection). The multiorifice injectors are unreliable at high loads, since the fuel reaches the cylinder walls without vaporizing or burning, and at low loads, since the performance of orifice sprays is very sensitive to the injection pressure, and the atomization of the fuel is poor at low injection pressures. Air swirl requires spending a significant fraction of the compression work into the generation of high air velocities, with the consequent reduction in thermal efficiency. Indirect injection inherently leads to larger heat losses, due to the larger surface area of the combustion chamber.
Gasoline injectors, while not being subject to the same stringent conditions of heat transfer and optimum dispersion required of diesel injectors, are subject to clogging problems that originate poor engine performance and high emissions when a three-way catalyst is used at the exhaust. Atomization is usually achieved by generating thin fuel sheets by pintle-type atomizers, or jets produced by small holes. Clogging is a problem because the pintle gap or typical orifice size is very small, and residues coming from evaporated fuel tend to accumulate in them. An injector generating a fine spray, with larger holes, and capable of supporting multiple orifices would minimize the clogging problem.
Finally, in other industrial processes, such as gas turbine combustion and spray painting, for instance, a flat spray of nearly uniform drop distribution is frequently sought. The current "fan" atomizers are simple, but the presence of obstacles in the upstream flow limit their clog-free operation. It is nearly always necessary to provide a flow of secondary air, either to help atomization, or to modify into a flat shape a spray that otherwise would have a circular cross-section.
Some atomizers (see, for instance U.S. Pat. No. 3,759,448) generate a "fan" spray by splitting the flow into two streams, that are caused to impinge at the orifice. However, this process requires a careful machining of parts, cannot easily support multiple orifices per injector, and is sensitive to clogging, due to the obstruction in the flow. Many other atomizers generating fan sprays need an air supply to feed the "horns" that shape the spray into a flat sheet.